One of the problems with fluid circuits in blood treatment systems is entrained air (bubbles) in treatment fluids, infusate, or blood. Treatment systems normally have air detectors to prevent air from being injected into a patient, either because a venous line carrying blood back to the patient contains air or because an infusate line, such as the replacement fluid line of a hemofiltration system, contains air. It is desirable for the air detectors to be made sufficiently sensitive to prevent the rare instances of long trains of air bubbles being injected into a patient. But sensitivity high enough to prevent long thin trains of bubbles may be high enough to alarm very small amounts of air which pose no risk. In other words, sensitive air detectors alarm on a lot of fall positives if they protect against all possible risks.
A prior art approach has been to remove as much air from a protected fluid circuit as possible. Putting air traps in fluid circuits, particularly blood lines, has drawbacks. Air-settling chambers necessarily involve stagnant flow, which creates a risk of forming clots (e.g., for blood) or sedimentation or other concentration of entrained material (e.g. medication).
Another prior art problem is stagnant flow in the headers of microtubular filter used for most dialyzers and hemofilters. This is a particular problem in the venous header where flow from many microtubules coalesces into a single slow moving flow.
The inventive embodiments provide various other features and advantages in addition to or in lieu of those discussed above and below. Many of these features and advantages are apparent from the description below with reference to the following drawing.